La–Zn Substituted Hexaferrites Prepared by Chemical Method

Abstract

La–Zn substituted M-type Ba hexaferrite powders were prepared by sol-gel (Mx) and organometallic precursor (Sk) methods with Fe/Ba ratio of 11.6 and 10.8, respectively. The compositions (LaZn) _x Ba_{1 − x} Fe_{12 − x} O₁₉ with 0.0 ≤ x ≤ 0.6 were annealed at 975°C/2 h. The cationic site preferences of nonmagnetic La³⁺ instead of Ba²⁺ ions and Zn²⁺ instead of Fe³⁺ ions were determined by Mössbauer spectroscopy. The La³⁺ ions substitute the large Ba²⁺ ions at 2a site and for x ≥ 0.4 also at 4f₂ site. The nearly all Zn²⁺ ions are placed at the 4f₁ sites. The thermomagnetic analysis of χ(ϑ) confirms that only the small substitutions for x ≤ 0.4 can be taken as a single-phase hexaferrites. The coercivity H _c almost does not change at x = 0.2 for (Mx) samples and further decrease up to x = 0.6. For (Sk) samples at substitution x = 0.2 the values of H _c are decreasing and at higher x the values nearly do not change. The Curie points, T _c, slowly decrease with x for both (Mx) and (Sk) samples.